1. Field of Invention
This invention relates to a method and system for the patterning wafers at high speed without the generation of a photomask.
2. Brief description of the Prior Art
In the production of integrated circuits, computer designed patterns are used to delineate areas on the circuit. For each item produced, up to twenty or more different patterns are used, i.e., one for each level of the circuit. There are currently two methods for transferring patterns onto semiconductor substrates.
The first method uses a glass plate with chrome and photosensitive layer on it. After the pattern is designed on the computer, a special camera is used to expose the photosensitive layer. The photosensitive layer is then developed and the chrome is etched away in the exposed area.
This mask is then used to pattern the intergrated circuit through the use of another camera. The camera aligns the photomask with the wafer and then floods the mask with light, allowing light only to pass through area where the chrome is removed, thus exposing the wafer. In this way the entire circuit is patterned all at one time. The advantage of this method is the speed in which the wafer can be exposed. In a production fabrication facility over 40 wafer are treated each hour for each for each patterning system.
A disadvantage of this system is that a new mask must be produced for each level of the circuit. This adds up to thousands of masks for a production facility. An other disadvantage is that the a new mask must be produced for any change of mask set.
Another method for patterning an integrated circuit is through the use of a beam writing tool. This tool uses a focused scan of particles, such as an electron beam, or an ion beam to expose the photosensitive material on the wafer. In this method, each circuit is exposed using a beam that is millions of times smaller than the area of the circuit. The beam then has to scan the entire surface area of the circuit. The advantage of this method is that the pattern being exposed on the wafer can be changed by varying the data fed into the beam writing tool. The need for creating a photomask first is eliminated. The disadvantage of the method is the speed at which the tool writes the patterns. With these systems, i.e., 6 wafers per hour can be run through the system. This is a problem in production where a level of 60 wafers per hour would be desirable.